Corrosion resistance in air bearing surfaces

ABSTRACT

A method includes identifying a microelectronic device located at an air bearing surface. The method further includes identifying a resistive heating element electrically isolated the said microelectronic device; applying a bias current through the resistive heating element to generate localized heat to heat the microelectronic device; identifying a predetermined humidity threshold and a separation distance between the microelectronic device and the resistive heating element in at least one dimension; measuring an ambient temperature at the air bearing surface; measuring an ambient relative humidity at the air bearing surface; determining an effective temperature; and adjusting the bias current to heat the microelectronic device to the effective temperature. The resistive heating element is one of a plurality, and at least two of the plurality of resistive heating elements are powered from a common source such that at least two of the resistive heating elements are commonly controllable via a common source.

BACKGROUND

The present invention relates generally to the field ofmicroelectronics, and more particularly to protecting air bearingmicroelectronic surfaces from corrosion.

Metal surfaces that are exposed to air are at risk of corrosion damagedue to corrosive agents in the environment. For microelectronicstructures, even small amounts of corrosion can lead to a failure of anydevice that includes air bearing surfaces. For example, magnetic tapehardware or hardware for accessing other magnetic media typicallyinclude air bearing tape reader and tape writer devices incorporatedinto a read and/or write head. While protective coatings are availablefor some applications, such coatings may wear off leaving a devicesurface exposed to air. Tape read/write heads may include variousair-exposed devices. Use of such devices often must be restricted to ahighly controlled environment, such as a climate-regulated data center.For applications where it is necessary to have less controlledconditions, engineers continue to face challenges in adequatelyprotecting from corrosion tape reader and tape writer devices as well asother air bearing microelectronic surfaces.

SUMMARY

A structure includes an air bearing surface, which includes a pluralityof material layers arranged in at least one dimension on the air bearingsurface. The structure further includes a microelectronic device and aresistive heating element, which each include at least one of theplurality of material layers. The resistive heating element iselectrically isolated from the microelectronic device. Themicroelectronic device is heated by said resistive heating element.

Optionally, the microelectronic device and the resistive heating elementare separated by an effective distance such that, for a predeterminedlevel of bias current passed through the resistive heating element, themicroelectronic device is heated at least to an effective temperaturewhereat relative humidity at that region of the air bearing surfacewhere the microelectronic device is located is reduced below apredetermined humidity threshold.

In an alternative aspect, a structure includes at least one of a tape atape writer or a tape reader, located at an air bearing surface. Thestructure further includes a resistive heating element. The resistiveheating element is electrically isolated from the at least one of a tapewriter or a taper reader. The at least one of a tape writer or a tapereader is heated by the resistive heating element.

Optionally, the at least one of a tape writer or a tape reader and theresistive heating element are separated by an effective distance suchthat, for a predetermined level of bias current passed through theresistive heating element, the at least one of a tape writer or a tapereader is heated at least to an effective temperature whereat relativehumidity at that region of the air bearing surface where the at leastone of a tape writer or a taper reader is located is reduced below apredetermined threshold.

In an alternative aspect, a method includes identifying amicroelectronic device located at an air bearing surface, identifying aresistive heating element, which is electrically isolated from themicroelectronic device, applying a bias current through the resistiveheating element to heat the microelectronic device.

Optionally, the method further includes identifying a predeterminedhumidity threshold, identifying a separation distance between themicroelectronic device and the resistive heating element in at least onedimension, determining an effective temperature for which relativehumidity at that region of the air bearing surface where themicroelectronic device is located is reduced below the predeterminedhumidity threshold, and adjusting the bias current such that themicroelectronic device is heated at least to the effective temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of the air bearing surface of a “piggyback” writerand reader device, in accordance with at least one embodiment of thepresent invention.

FIG. 2 is a plan view of a generic microelectronic device and resistiveheater, in accordance with at least one embodiment of the presentinvention.

FIG. 3 is a simplified schematic view of a writer and resistive heatingdevice, in accordance with at least one embodiment of the presentinvention.

FIG. 4 is a simplified schematic view of a generic microelectronicdevice and resistive heater, in accordance with at least one embodimentof the present invention.

FIG. 5 is a simplified schematic view of multiple resistive heaterspowered from a common power source, in accordance with at least oneembodiment of the present invention.

FIG. 6 is a set of optical microscopy images depicting various“piggyback” writer and reader devices of an experimental example of atleast one embodiment of the present invention.

FIG. 7 is a graph of data from an experimental example of at least oneembodiment of the present invention.

FIG. 8 is a simplified schematic view of a tape drive system, inaccordance with at least one embodiment of the present invention.

FIG. 9 is a simplified schematic view of multiple tape interactiondevices, in accordance with at least.

FIG. 10 is a flowchart diagram for various operations of a method, inaccordance with at least one embodiment of the invention.

FIG. 11 is a flowchart diagram for additional operations of a method, inaccordance with at least one embodiment of the present invention.

FIG. 12 is a flowchart diagram for additional operations of a method, inaccordance with at least one embodiment of the present invention.

FIG. 13 is a block diagram depicting various logical elements for acomputer system capable of executing program instructions, in accordancewith at least one embodiment of the present invention.

DETAILED DESCRIPTION

Various microelectronic devices, such as the reading and writingapparatus of magnetic tape drive storage devices, include an air bearingsurface. Such surfaces are at risk of corrosion due to the combinedinteraction of corrosive ionic material with the surface metal materialand water. Sensitive microelectronic devices which are directly exposedto the atmosphere can become corroded if the atmosphere contains evensmall amounts of a corrosive agent, resulting in performance degradationor failure. For magnetic read/write heads used to store and read-backdata on magnetic media, very low levels of corrosion can result indamage, for example by Wallace spacing losses for read amplitudes orwrite field magnitudes and/or reduced magnetic moment of the writer atthe air-bearing-surface. Ionic corrosion from gases such as HCl and H₂Srequire at least a layer of water molecules (e.g., a monolayer) totransport the ions to the exposed metals and to catalyze the chemicalreaction. Thus, many damaging chemical reactions will not take place inan environment where the relative humidity (RH) is sufficiently low asto inhibit the formation of a layer of moisture on the metal surface.For some applications, it is possible to carefully control the relativehumidity a sufficiently low level, thereby keeping the metal at the airbearing surfaces (e.g., of tape or hard disk heads) sufficiently dry soas to prevent corrosive chemical reactions, regardless of the present ofionic material. For various other applications, it is not possible toprovide a controlled environment, and corrosion protection requiresother means.

Heating the metals at an air bearing surface locally can raise themetals' temperature sufficiently to reduce local relative humidity tobelow a critical threshold below which it is not possible to form acontinuous layer of moisture on the metal surface, and thus inhibiting ocorrosion. Many microelectronic devices have an innate electricalresistance so as to be susceptible to resistive heating (Joule heating)by applying a bias current through the material. For example, tape drivereader devices can be heated in this way by applying a bias current whenthe reader is not in use for reading from a tape. In the context of thepresent invention, the term “tape” principally means a magnetic tapesuitable for storing data in the form of magnetic bits. Tapes havingdifferent or unconventional electromagnetic properties, includingnonmagnetic tapes, may, however, potentially interact with air bearingmicroelectronic devices, and are thus also contemplated. Other devices,such as tape writer devices, may either be damaged if directly heated inthis way or may have no practical means of being self-heated. Suchdevices may be understood to not be able to functionally carry current.In the context of the present invention, a “piggyback” combined readerand writer device may be equipped with a resistive heating element as acomponent of the reader. The writer device may be warmed indirectly bylocalized heat from the reader without passing a bias current throughthe writer itself. More generally, a microelectronic device at an airbearing surface may be positioned proximate to a distinct andelectrically isolated resistive heater, which may receive a bias currentto generate localized heat, indirectly heating the microelectronicdevice.

FIGS. 8 and 9 identify the general layout of a tape drive system, inaccordance with some embodiments of the present invention. FIG. 8presents a simplified schematic side view of a tape drive systemincluding the tape 800, which is spooled between two reels 802 to runover a read and/or write head 804. FIG. 9 presents a simplifiedschematic plan view of various air bearing microelectronic structures ofa reading and/or writing device. In FIG. 9, the tape 800 may beunderstood to be positioned above the read/write head 900, relative tothe viewer, and to be movable forward or backward in at least onedimension, the dimension of media travel 990. The cutaway portion ofFIG. 9 represents the different possible widths of the tape 800 andcorrespondingly different possible numbers of readers 902 and writers904. In some embodiments, sixteen devices may be positioned across thewidth of the tape 800. Each reader 902 may include a resistive heatingelement 903. The reader 902 may be combined with a writer 904 into a“piggyback” structure 906. Such that the writer 904 is heated indirectlyby the resistive heating element 903.

Referring now to FIG. 1, FIG. 1 depicts a plan view of an air bearingsurface 100 including a combined “piggyback” reader and writer. The airbearing surface 100 includes microelectronic structures arranged in afirst dimension 190 with various structures aligned with reference to anaxis 194. A tape, such as the tape 800, may be understood to be elevatedabove the air bearing surface 100, relative to the viewer of FIG. 1,with the tape movable in at least one dimension. Specifically, the tapemay be movable forward and backward in the first dimension 190, and maybe fixed in position in a second dimension 192, which may beperpendicular to the first dimension 190 in a plane with the depictedair bearing surface 100 (although, the air bearing surface need notnecessarily be flat in all embodiments of the present invention).

Referring still to FIG. 1, the air bearing surface 100 includes a firstsubstrate layer 110 and a second substrate layer 114, above and belowthe various devices, as shown. The first substrate layer 110 and secondsubstrate layer 114 may be composed of ceramic substrate material. Afirst dielectric layer 112 may surround the various devices of theinvention and a second dielectric layer 115 may lie between the variousdevices and the second substrate layer 114. The first dielectric layer112 and second dielectric layer 115 may be joined distally around theedges of the various devices, and they may be composed of alumina orsimilar dielectric material.

Referring still to FIG. 1, a first tape reader metal element 132 mayoppose a second tape reader metal element 134, both centered withreference to the axis 194, which forms an axial line for the depicteddevices. The first tape reader metal element 132 and second tape readermetal element 134 may be configured for reading from a tape, such as thetape 800, according to known structures and methods, for example ascomponents of a magnetoresistive reader. Both the first tape readermetal element 132 and the second tape reader metal element 134 may becomposed of copper or other conductive material. In the depictedembodiment, the first tape reader metal element 132 and second tapereader metal element 134 are separated by one or more tape readerdielectric layers 136, which are positioned distally on either side ofthe axial line, as shown. Centrally, as to the axial line of the axis194, the first tape reader metal element 132 and the second tape readermetal element 134 may be separated by the resistive heating element 130,which may include or be composed of a thin film resistor. Together, thefirst tape reader metal element 132, the second tape reader metalelement 134, and the resistive heating element 130 may form a tapereader. Accordingly, the tape reader may be understood to include theresistive heating element 130. The tape reader may further be understoodto be configured to read from the tape 800. The resistive heatingelement 130 may be separated from the reader elements such as the firsttape reader metal element 132 and the second tape reader metal element134 by thin layers of alumina or other dielectric, however thesebarriers need not separate the tape reader from the resistive heatingelement to the same degree as for the tape writer, which does notfunctionally carry current.

Referring still to FIG. 1, a first electromagnetic pole element 120 mayoppose a second electromagnetic pole element 122, separated by a writegap 124, which may include a layer of alumina or similar dielectricmaterial. The first electromagnetic pole element 120 and secondelectromagnetic pole element 122 may be in electromagneticcommunication, below the air bearing surface 100 in a mannercontrollable by a coil such that a magnetic field may be generated withsufficient strength and uniformity above the write gap 124 for writingto a tape, such as the tape 800, according to known structures andmethods, for example as components of an inductive writer. The firstelectromagnetic pole element 120 and second electromagnetic pole element122 may be constructed of a soft magnetic material such as Nickel-Iron(45:55 NiFe, etc.). Some writers may use a laminate of differentmagnetic alloys. The first electromagnetic pole element 120 and secondelectromagnetic pole element 122 together may form a tape writer. Thetape writer may be understood as configured for writing to the tape 800.

Referring still to FIG. 1, the tape writer may be electrically isolatedfrom the tape reader by an isolation dielectric layer 116. The tapewriter may be proximate to the tape reader such that the resistiveheating element 130, included in the tape reader, heats the tape writer.In the depicted embodiment, an effective distance 150 separates theresistive heating element 130 from the second electromagnetic poleelement 122, as described further below.

Referring now to FIG. 2, more generally, the invention may be applied toa microelectronic device at an air bearing surface 200. The air bearingsurface 200 may include a plurality of material layers, arranged in atleast one dimension, such as the dimension 290, on the air bearingsurface 200. The plurality of material layers may include a firstsubstrate layer 210 and a second substrate layer 214, which may both becomposed of e.g., a ceramic substrate material. Analogously to FIG. 1, afirst dielectric layer 212 and a second dielectric layer 215 may liebetween the various devices and the first substrate layer 210 and/orsecond substrate layer 214, which may be composed of alumina. Amicroelectronic device 220 may include at least one of the plurality oflayers. As depicted, the microelectronic device may include variouscombinations of metal and dielectric layers, similarly to the writer ofFIG. 1. A resistive heating element 230, such as a thin film resistor,may also comprise at least one of the plurality of layers. The resistiveheating element 230 may be incorporated into a directly heatable device232, which may include one or more of the plurality of layers and may beunderstood as analogous to the tape reader of FIG. 1. The resistiveheating element 230 may be electrically isolated from themicroelectronic device 220, for example, by an isolation dielectriclayer 216. In the depicted embodiment, an effective distance 250separates the resistive heating element 130 from the secondelectromagnetic pole element 122, as described further below.

Referring still to the embodiment depicted in FIG. 2, themicroelectronic device 220 is heated, indirectly, by localized heat fromthe resistive heating element 230. In the context of the presentinvention, to be heated indirectly means receiving at least one ofradiant, conductive, or convective heat without being in direct contactsuch that the received heat is mediated through (or, in the case ofradiant heating, passes through) the material(s) of the plurality oflayers or through air or other surrounding material. Accordingly, in atleast some embodiments, the microelectronic device 220 and the resistiveheating element 230 may be understood as distinct structures such thatthe resistive heating element 230 is not incorporated into themicroelectronic device 220, even as the resistive heating element 230may be incorporated into another device, such as the directly heatabledevice 232. Equivalently, some embodiments may be such that themicroelectronic device 220 is not susceptible to direct heating.

FIGS. 3 and 4 provide a simplified schematic understanding of variousembodiments of the invention. FIG. 3 displays a first electromagneticpole element 302 opposing a second electromagnetic pole element 304 toform a tape writer. Both are proximate to, but not in contact with, aresistive heating element 300. Similarly, FIG. 4 depicts an abstractedmicroelectronic device 402, of generally any kind, proximate to aresistive heating element 400. For both FIGS. 3 and 4, the simplifieddevices shown, at an air bearing surface, would be protected fromcorrosion by localized heating.

Additionally, FIG. 3 demonstrates how a writer including the firstelectromagnetic pole element 302 and the second electromagnetic poleelement 304 may be packaged with the resistive heating element 300 intoa module 310. The module 310 may be understood as the writer-heatercombination for incorporation into a tape head or other larger device.Similarly, the generic, abstracted microelectronic device 402 may bepackaged, together with the resistive heater 400, into a module 410 forinclusion into a larger device. In some embodiments, the abstractedmicroelectronic device 402 may be a tape reader, for example, whereproject-specific considerations prevent the reader from beingself-heated, as per FIG. 1. Within the field of tape interactiondevices, a resistive heating element and at least one of a tape readerand a tape writer may be packaged together as a module. More generally,a resistive heating element and any microelectronic device may bepackaged together as a module.

Referring now to FIG. 5, a first resistive heating element 500 and asecond resistive heating element 510 may be present in the same system.FIG. 9 depicts an example of a system wherein the resistive heatingelement 903 is one of a plurality of resistive heating elements. Thefirst resistive heating element 500 may be in electrical communicationwith a first lead 502 and a second lead 504. Similarly, the secondresistive heating element 510 may be in electrical communication withthe first lead 512 and a second lead 514. A common source such as thecommon power source 520 may be in electrical communication with a powersource first lead 522 and a power source second lead 524. By connectingthe first leads 502 and 512 with the power source first lead 522, and byconnecting the second leads 504 and 514 with the power source secondlead 524, as shown, at least two of a plurality of resistive heatingelements (e.g., 500 and 510) may be powered in from the common powersource 520 such that the at least two of the plurality of resistiveheating elements (e.g., 500 and 510) are commonly controllable via thecommon power source 520. The depicted configuration permits uniformresistive heating for all heaters and protected devices for a givenstructure. FIG. 5 depicts a circuit in which the heating elements 500and 510 are configured in parallel, however alternatives includeconfiguring the heaters in series or a combination of series andparallel, according to engineering considerations to have desiredelectrical properties for the particular embodiment.

Various configurations may provide bias currents at each heater that areequal to one another, approximately equal to one another, or differentlyproportional to current through the common power source 520. Practicalreasons for selecting one connection type or another include, formultiple resistive elements (e.g., 500, 510), whether the resistiveelements need to be powered identically such that the same total poweris consumed for each resistive heating element. However, if the heatingelements are connected in series, the voltage required increaseslinearly with the number of heating elements. It is possible that thecommon power source 520 will not have sufficient voltage available. Bycontrast, when connecting the resistive elements in parallel, thecurrent required increases linearly with the number of heating elements,and the common power source 520 may be limited in the amount of currentwhich it can supply. More complex configurations may include creatingmultiple groups of multiple resistive heater, with the heaters withinthe group configured in series and the groups configured in parallel.Thus, a common power supply may be designed for larger numbers ofheating elements. For example, with thirty resistive elements, onepossible configuration includes connecting six groups of five resistiveheaters each in series within each group, with the six groups inparallel. In this case, the voltage supplied to each group would be fivetimes the amount applied across each individual heater, and the totalcurrent would be only six times the current through each individualheater. In the stated example, if the heaters were all connected inparallel, the total current would have been thirty times the currentthrough each individual heater, while if the heaters had been connectedin series, the voltage required would have been thirty times the voltageacross an individual heater.

In general, the various embodiments of the invention may include passinga bias current through the heating element 230 to heat themicroelectronic device 220. The value of the bias current may be variedby varying the voltage applied, given a fixed resistance of theresistive heating element 230 for a given embodiment. Equivalently,variations in the structure and material properties of the resistiveheating element relate to the amount of localized heat that is emitted.Additionally, the distance between the resistive heating element 230 andthe microelectronic device 220 affects the amount of localized heatreaching the microelectronic device. In various embodiments, themicroelectronic device 220 and the resistive heating element 230 may beseparated by an effective distance 250 such that, for a predeterminedlevel of bias current passed through the resistive heating element, themicroelectronic device is heated at least to an effective temperaturewhereat relative humidity at that region of the air bearings surface 200where the microelectronic device is located is reduced below apredetermined humidity threshold.

Equivalently, and with reference to the embodiment depicted in FIG. 1,the tape writer and the resistive heating element 130 may be separatedby an effective distance 150 such that, for a predetermined level ofbias current passed through the resistive heating element 130, the tapewriter is heated at least to an effective temperature whereat relativehumidity at that region the air bearing surface 100 where the tapewriter is location is reduced below a predetermined threshold.

Referring now to FIG. 6, the inventors conducted an experiment based onthe present invention. A row bar including multiple self-similarstructures (similar to the embodiment depicted in FIG. 1) was cabled sothat each resistive heating elements could be powered separately. Therow bar was placed in a humidity chamber at relative humidity of 84%.Each resistive heating element was characterized by a resistance ofapproximately 100 ohms. Various structures were powered with currents of1 mA, 3 mA, 4 mA, and 6 mA. HCl gas was injected into to the 2 literchamber to a projected equilibrium concentration of 20 ppm (if all HClremained gaseous). FIG. 6 displays optical microscopy images for variousstructures at various levels of bias current. It is apparent from themicroscopy images that the write structures were markedly less corrodedwhere a larger bias current was applied to the heater (e.g., 6 mA) thanwhere a smaller bias current as applied (e.g., 1 mA). In particular, at6 mA bias current, there was virtually no corrosion at the write gap.FIG. 7 displays the observed thermal profile of the test devices aslocal temperature in relation to distance offset from the resistiveheater in the dimension corresponding to the direction of tape movement.

To understand the Joule heating of metals which do not have heatingcurrent flowing through them, the inventors performed finite elementanalysis (FEA) calculations using the plausible thermal conductivity thealumina surrounding the heater and the metals themselves. The results ofthe FEA were that the temperature rise of the heater (ΔT_(htr)) isproportional to the power deposited into the heater (P_(htr)):

$\begin{matrix}{{\Delta\; T_{htr}} = \frac{P_{htr}}{\kappa_{htr}}} & {{Equation}\mspace{14mu} 1}\end{matrix}$κ_(system)=κ₀+κ_(A) ·A _(htr)   Equation 2

κ_(htr) is the thermal conductance of the heater structure and itssurroundings. κ_(o) and κ_(A) are a constants related to the thermalconductivity of the metals surrounding the heater, and A_(htr) is thearea to be heated. The inventors have observed Equation 2 to bedescriptive for areas on the order of 1 μm² with values of κ_(o)=14 mW/°C. and κ_(A)=42 mW/° C./μm². The metals surrounding the heater may alsobe heated through thermal conduction from heat source of the resistiveheating element to the surrounding metals. The heat may diffuse from theheater to the metals surrounding the heater. The temperature rise of thesurrounding metal, ΔT_(M), is also linear with P_(htr):

$\begin{matrix}{{\Delta\; T_{M}} = {\frac{P_{htr}}{\kappa_{htr}} = {{C_{M} \cdot T_{htr}} = {{\frac{\kappa_{htr}}{\kappa_{M}} \cdot \Delta}\; T_{htr}}}}} & {{Equation}\mspace{14mu} 3}\end{matrix}$

$\begin{matrix}{C_{M} = \frac{\kappa_{htr}}{\kappa_{M}}} & {{Equation}\mspace{14mu} 4}\end{matrix}$

Table 1 gives the relevant values of the thin-film metal heater fordetermining the temperature rise, and the calculated temperature riseusing finite element analysis (FEA). At 6 mA, the heating is calculatedto be 45° C., and at 1 mA, 1° C., supporting the concept that theheating is protecting the devices. The value of less than 30% RH waschosen by the inventors because they observed and/or recognized that therate of corrosion of the thin metals used in magnetoresistive (MR)readers and tape writers is essentially arrested even for very highlevels of corrosive gases (e.g., ˜10 ppm of HCl gas). The inventors havefurther observed and/or recognized that reducing RH into the range of60%-70% will significantly decrease corrosion rates and can thus offerprotection against corrosion. Additionally, RH in the range of 30%-60%may be expected to have an intermediate effect.

TABLE 1 ΔT_(htr) ΔT_(htr) ΔT_(htr) ΔT_(htr) R_(htro) P_(htr) Area (1 mA)(3 mA) (4 mA) (6 mA) (ohm) (mW) (um2) (° C.) (° C.) (° C.) (° C.) 652.25 0.90 1.3 11.2 20.0 45

Table 2 shows the Joule heating temperature required to reduce the localrelative humidity of the heater to below 30% (an exemplary relativehumidity threshold) to protect the heater from corrosion when theambient temperature and ambient relative humidity are T_(air) andRH_(air), respectively.

TABLE 2 RH_(air) T_(air) (° C.) 20 25 30 35 40 50 40% ΔT_(M) (° C.) 5.15.3 5.5 5.6 5.8 6.0 50% ΔT_(M) (° C.) 9.1 9.4 9.7 10.0 10.3 10.6 60%ΔT_(M) (° C.) 12.3 12.7 13.1 13.4 14.0 14.5 70% ΔT_(M) (° C.) 15.0 15.516.0 16.6 17.1 17.6 80% ΔT_(M) (° C.) 17.4 18.0 18.6 19.2 19.8 20.4 90%ΔT_(M) (° C.) 19.5 20.1 20.8 21.5 22.2 22.9

The heating required may be set more precisely if the relative humidityis known. Equation 5 shows a quadratic expression used to fit thesaturation vapor density (V_(sat)) versus temperature:V _(sat)(T _(C))=V _(S0) +V _(S1) ·T _(C) +V _(S2) ·T _(C)²=24.164−1.257T _(C)+0.48T _(C) ²   Equation 5

T_(C) is the temperature in degrees Celsius. The saturation volume wasfit to a quadratic expression. The relative humidity may be understoodas the actual vapor density, V_(moisture), divided by the saturationvapor density:

$\begin{matrix}{{RH} = \frac{V_{moisture}}{V_{sat}}} & {{Equation}\mspace{14mu} 6}\end{matrix}$

If T_(env) is known, then Equation 5 becomesV_(sat-env)=V_(sat)(T_(env)). If the environmental relative humidity(RH_(env)) is known, then the moisture level is described as:V _(moisture) =RH _(env) ·V _(sat)(T _(env))   Equation 7

If the local temperature of the device being protected is increased byΔT_(dev) above T_(env), then the local relative humidity, RH_(loc), isgiven by:

$\begin{matrix}{{R\; H_{loc}} = {\frac{V_{moisture}}{V_{sat}( {T_{env} + {\Delta\; T_{dev}}} )} = {R\;{H_{env} \cdot \frac{V_{sat}( T_{env} )}{V_{sat}( {T_{env} + {\Delta\; T_{dev}}} )}}}}} & {{Equation}\mspace{14mu} 8}\end{matrix}$

Or, to achieve a desired RH_(loc):

$\begin{matrix}{{V_{sat}( {T_{env} + {\Delta\; T_{dev}}} )} = {{V_{sat}( T_{env} )} \cdot \frac{R\; H_{env}}{R\; H_{loc}}}} & {{Equation}\mspace{14mu} 10}\end{matrix}$

$\begin{matrix}{{{{( {V_{s\; 1} + {2 \cdot V_{s\; 2} \cdot T_{env}} + V_{s\; 2}} ) \cdot \Delta}\; T_{dev}} + {{V_{s\; 2} \cdot \Delta}\; T_{htr}^{2}}} = {{V_{sat}( T_{env} )} \cdot \frac{{R\; H_{env}} - {R\; H_{loc}}}{R\; H_{loc}}}} & {{Equation}\mspace{14mu} 11}\end{matrix}$

$\begin{matrix}{{\Delta\; T_{dev}} = \frac{{- B} + \sqrt{B^{2} - {4 \cdot A \cdot C}}}{2 \cdot A}} & {{Equation}\mspace{14mu} 12a}\end{matrix}$A=V _(s2)  Equation 12bB=V _(s1)+2·V _(s2) ·T _(env) +V _(s2)  Equation 12c

$\begin{matrix}{C = {{- {V_{sat}( T_{env} )}} \cdot \frac{{R\; H_{env}} - {R\; H_{loc}}}{R\; H_{loc}}}} & {{Equation}\mspace{14mu} 12d}\end{matrix}$

Equations 12a, 12b, 12c, and 12d demonstrate how the quadratic formulamay be applied to Equation 11 to solve for ΔT_(dev), the effectivetemperature rise to reduce corrosion in a given device to below arelative humidity threshold. Thus, where both the environmentaltemperature, T_(env), and relative humidity, RH_(env), are measured, thelocal relative humidity, RH_(local), versus local temperature,T_(local), may be calculated using the above polynomial function fromknown values of saturation vapor density. The Joule heating temperaturerise of the metal being protected, ΔT_(M), required to achieve aparticular RH_(local) is determined from the polynomial. The Jouleheating temperature rise (ΔT_(htr)) versus power into the heater,P_(htr), is determined such that:

$\begin{matrix}{{\Delta\; T_{htr}} = \frac{P_{htr}}{\kappa_{htr}}} & {{Equation}\mspace{14mu} 13}\end{matrix}$

In Equation 13, κ_(htr) is a parameter termed the conductance, and itdepends on the thermal properties and geometries of the materialssurrounding the heater. The fractional temperature rise of the metalbeing protected ΔT_(M) is determined such that:

$\begin{matrix}{{\Delta\; T_{M}} = {{f_{M}\Delta\; T_{htr}} = {f_{M}\frac{P_{htr}}{k_{htr}}}}} & {{Equation}\mspace{14mu} 14}\end{matrix}$

In Equation 14, f_(M) is a fraction less than unity and depends on thematerials surrounding the metal and separating the metal from the heaterand the geometry and thermal properties of the metal itself. Theseparameters are used to determine the necessary power into the heater toachieve the particular RH_(local).

The Joule heating temperature rise of the writer pole may be determinedto be a fraction of the temperature rise of the metal film used to heatthe writer pole through diffusion. The fractional amount ispredetermined. The temperature rise of the heating element may bemeasured by the resistance change of the heating element, which may beused to determine the temperature of the distant writer pole. Thetemperature rise of the writer pole may be determined using finiteelement calculations or by some optical thermometry measurement or someother physical measurement.

FIG. 10 is a flowchart diagram depicting various operations for a methodaccording to the present invention. The described method may becontrolled or mediated by a computer as a heater control program 1001,or the method may be performed independently of any computer. Atoperation 1000, the method includes identifying a microelectronic device220. The microelectronic device may be located at an air bearing surface200. At operation 1010, the method includes identifying a resistiveheating element 230. The resistive heating element 230 may beelectrically isolated from the microelectronic device 220. At operation1020, the method includes applying a bias current through the resistiveheating element 230 to generate localized heat. At operation 1030, themethod includes heating the microelectronic device 220 by the localizedheat.

FIG. 11 is a flowchart diagram depicting additional operations for themethod according to the present invention. At operation 1100, the methodincludes identifying a predetermined humidity threshold. Thepredetermined humidity threshold may be chosen, based onproject-specific and material-specific considerations at a value atwhich corrosion is expected to be inhibited by the above-discussedprocesses and effects. In the above-discussed example, a local relativehumidity of 30% at an air bearing surface may be deemed sufficient, forsome embodiments to prevent corrosion at the air bearing surface. Othervalues for a humidity threshold may be chosen in other contexts,including non-static varying values or relative humidity criteriaaccording to a rejection curve, etc. At operation 1110, the methodincludes identifying a separation distance 250 between themicroelectronic device 220 and the resistive heating element 230 in atleast one dimension 290. At operation 1120, the method includesdetermining an effective temperature for which relative humidity at thatregion of the air bearing surface 200 where the microelectronic deviceis located is reduced below the predetermined humidity threshold.Determining the effective temperature may be accomplished according toany of the means described above. At operation 1130, the method includesadjusting the bias current such that the microelectronic device 220 isheated at least to the effective temperature, thereby preventingcorrosion of the microelectronic device.

FIG. 12 is a flowchart diagram depicting additional operations for themethod according to the present invention. At operation 1200, the methodincludes measuring an ambient temperature at the air bearing surface200. The measurement may be accomplished by any of the above-describedmeans. Still at operation 1200, the method includes measuring an ambientrelative humidity at the air bearing surface 200. The measurement may beaccomplished by any of the above-described means. Further, measurementstaken “at” the air bearing surface 200 include measurements taken nearor proximate to the air bearing surface, such that the measured valueprovides a reasonable estimate of the true value at the air bearingsurface 200, an in particular, at the microelectronic device 220. Atoperation 1210, more specifically than at operation 1120, determiningthe effective temperature is based on the ambient temperature and theambient humidity, according to the means described above. At operation1220, the method includes determining an effective temperature rise,based on the ambient temperature and the effective temperature, forexample, as described above, by subtracting the ambient temperature fromthe effective temperature to yield the amount by which the localtemperature must rise to reach the effective temperature. At operation1230, the method includes increasing the bias current such that themicroelectronic device is heated by at least the effective temperaturerise.

Accordingly, the present invention may be understood as including one ormore methods of operating the structures described above, whethermanually, by computer-controlled automation, or otherwise. Acomputerized controller may include a computer, such as the exemplarycomputer 1300 according to FIG. 13, which may be incorporated into thehardware companying the microelectronic device 220 and resistive heatingelement 230, and the leads of one or more resistive heating elements 230may be placed in electronic communication and/or control, for examplethrough the I/O interfaces 1312 as external devices 1318, or otherwise.Program instructions for the computerized controller may be understoodas a heater control program 1001, which may perform the operations ofthe methods of the invention. However, it will be appreciated that theoperations of the method(s) disclosed herein include the electrical andphysical operation of the structures recited, and they need not beperformed with the assistance of any computer.

FIG. 13 is a block diagram depicting components of a computer 1300suitable for executing the heater control program 1001. FIG. 13 displaysthe computer 1300, the one or more processor(s) 1304 (including one ormore computer processors), the communications fabric 1302, the memory1306, the RAM, the cache 1316, the persistent storage 1308, thecommunications unit 1310, the I/O interfaces 1312, the display 1320, andthe external devices 1318. It should be appreciated that FIG. 13provides only an illustration of one embodiment and does not imply anylimitations with regard to the environments in which differentembodiments may be implemented. Many modifications to the depictedenvironment may be made.

As depicted, the computer 1300 operates over a communications fabric1302, which provides communications between the cache 1316, the computerprocessor(s) 1304, the memory 1306, the persistent storage 1308, thecommunications unit 1310, and the input/output (I/O) interface(s) 1312.The communications fabric 1302 may be implemented with any architecturesuitable for passing data and/or control information between theprocessors 1304 (e.g., microprocessors, communications processors, andnetwork processors, etc.), the memory 1306, the external devices 1318,and any other hardware components within a system. For example, thecommunications fabric 1302 may be implemented with one or more buses ora crossbar switch.

The memory 1306 and persistent storage 1308 are computer readablestorage media. In the depicted embodiment, the memory 1306 includes arandom access memory (RAM). In general, the memory 1306 may include anysuitable volatile or non-volatile implementations of one or morecomputer readable storage media. The cache 1316 is a fast memory thatenhances the performance of computer processor(s) 1304 by holdingrecently accessed data, and data near accessed data, from memory 1306.

Program instructions for the heater control program 1001 may be storedin the persistent storage 1308 or in memory 1306, or more generally, anycomputer readable storage media, for execution by one or more of therespective computer processors 1304 via the cache 1316. The persistentstorage 1308 may include a magnetic hard disk drive. Alternatively, orin addition to a magnetic hard disk drive, the persistent storage 1308may include, a solid state hard disk drive, a semiconductor storagedevice, read-only memory (ROM), electronically erasable programmableread-only memory (EEPROM), flash memory, or any other computer readablestorage media that is capable of storing program instructions or digitalinformation.

The media used by the persistent storage 1308 may also be removable. Forexample, a removable hard drive may be used for persistent storage 1308.Other examples include optical and magnetic disks, thumb drives, andsmart cards that are inserted into a drive for transfer onto anothercomputer readable storage medium that is also part of the persistentstorage 1308.

The communications unit 1310, in these examples, provides forcommunications with other data processing systems or devices. In theseexamples, the communications unit 1310 may include one or more networkinterface cards. The communications unit 1310 may provide communicationsthrough the use of either or both physical and wireless communicationslinks. The heater control program 1001 may be downloaded to thepersistent storage 1308 through the communications unit 1310. In thecontext of some embodiments of the present invention, the source of thevarious input data may be physically remote to the computer 1300 suchthat the input data may be received and the output similarly transmittedvia the communications unit 1310.

The I/O interface(s) 1312 allows for input and output of data with otherdevices that may operate in conjunction with the computer 1300. Forexample, the I/O interface 1312 may provide a connection to the externaldevices 1318, which may include a keyboard, keypad, a touch screen,and/or some other suitable input devices. External devices 1318 may alsoinclude portable computer readable storage media, for example, thumbdrives, portable optical or magnetic disks, and memory cards. Softwareand data used to practice embodiments of the present invention may bestored on such portable computer readable storage media and may beloaded onto the persistent storage 1308 via the I/O interface(s) 1312.The I/O interface(s) 1312 may similarly connect to a display 1320. Thedisplay 1320 provides a mechanism to display data to a user and may be,for example, a computer monitor.

The programs described herein are identified based upon the applicationfor which they are implemented in a specific embodiment of theinvention. However, it should be appreciated that any particular programnomenclature herein is used merely for convenience, and thus theinvention should not be limited to use solely in any specificapplication identified and/or implied by such nomenclature.

The present invention may be a system, a method, and/or a computerprogram product at any possible technical detail level of integration.The computer program product may include a computer readable storagemedium (or media) having computer readable program instructions thereonfor causing a processor to carry out aspects of the present invention.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, configuration data for integrated circuitry, oreither source code or object code written in any combination of one ormore programming languages, including an object oriented programminglanguage such as Smalltalk, C++, or the like, and procedural programminglanguages, such as the “C” programming language or similar programminglanguages. The computer readable program instructions may executeentirely on the user's computer, partly on the user's computer, as astand-alone software package, partly on the user's computer and partlyon a remote computer or entirely on the remote computer or server. Inthe latter scenario, the remote computer may be connected to the user'scomputer through any type of network, including a local area network(LAN) or a wide area network (WAN), or the connection may be made to anexternal computer (for example, through the Internet using an InternetService Provider). In some embodiments, electronic circuitry including,for example, programmable logic circuitry, field-programmable gatearrays (FPGA), or programmable logic arrays (PLA) may execute thecomputer readable program instructions by utilizing state information ofthe computer readable program instructions to personalize the electroniccircuitry, in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the blocks may occur out of theorder noted in the Figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

What is claimed is:
 1. A method comprising the steps of: identifying amicroelectronic device, said microelectronic device being located at anair bearing surface; identifying a resistive heating element, saidresistive heating element being electrically isolated from saidmicroelectronic device; applying a bias current through said resistiveheating element to generate localized heat; heating said microelectronicdevice by said localized heat; identifying a predetermined humiditythreshold; identifying a separation distance between saidmicroelectronic device and said resistive heating element in at leastone dimension; measuring an ambient temperature at said air bearingsurface; measuring an ambient relative humidity at said air bearingsurface; determining an effective temperature for which relativehumidity at that region of said air bearing surface where saidmicroelectronic device is located is reduced below said predeterminedhumidity threshold, based on said ambient temperature and said ambientrelative humidity; determining an effective temperature rise, based onsaid ambient temperature and said effective temperature; and adjustingsaid bias current such that said microelectronic device is heated atleast to said effective temperature by increasing said bias current suchthat said microelectronic device is heated by at least said effectivetemperature rise; and, wherein: said resistive heating element and saidmicroelectronic device are distinct structures; said resistive heatingelement comprises a thin film resistor; said resistive heating elementis one of a plurality of resistive heating elements; at least two ofsaid plurality of resistive heating elements are powered from a commonsource such that said at least two of said plurality of resistiveheating elements are commonly controllable via said common source.